RU2010870C1 - Method of thermal treatment of cutting tools made of high-speed steel - Google Patents

Abstract

FIELD: metallurgy. SUBSTANCE: novel method included two steps of thermal treatment. First, tools were many times heated to temperature of 610 C A₁ and oil cooled, repeatedly heated and cooled within temperature range from melting point and temperature at which martensite transformations began. Tools were then finally hardened from temperature of last heating in thermal treatment and annealing. At the second stage of thermal treatment, tools were isothermally processed in chloride melt in which carbonate and carbide were additionally introduced. Barium or potassium carbonate was employed as above mentioned carbonate and silicon or potassium carbide was used as above carbide. Using disclosed method of thermal treatment gave rise to reduction of structural components, great structural homogeneity, and high degree of alloying of solid solution by chemical elements. EFFECT: substantially higher durability of wood-cutting tools. 2 cl, 2 tbl

Description

 The invention relates to heat treatment of a woodworking tool made primarily of forged high-speed steel, and can be used in woodworking enterprises of local industry.

A known method of heat treatment of cast high speed steel, which includes preliminary and final heat treatment. Prebaked thermocyclic effected by heating to a temperature of 20-50 ^{° C} below the melting temperature, cooling to 800-850 ^{° C} with isothermal exposures 5-12 and 10-25 respectively with mm section. The final heat treatment is carried out by quenching and tempering according to standard conditions, combining quenching with the last heating to the upper temperature during thermal cycling. In order to ensure a high machinability preform cooling with lower temperature thermocycling to produce ^about 700-750 C, held 4-8 hours and finally cooled (1).

 The application of this method leads to crushing of the eutectic carbide network into individual carbide particles, to their spheroidization, increase the strength and heat resistance of cast high-speed steel.

 The specified method is characterized by low wear resistance of a woodworking tool.

 This is due primarily to the fact that the purpose of this method is to eliminate the carbide eutectic net, which is inherent only in cast high-speed steel, and for the forged and annealed high-speed steel with a carbide mesh already mechanically crushed, the known method is simply not applicable.

The closest to the proposed is a method of heat treatment of cutting tools of high speed steel, comprising temperature cycling by repeated heating to a temperature 60 ° ^C below the melting and cooling temperature to a temperature in the range of M _n - 660 ^{° C,} the final hardening of the latter the heating temperature during thermal cycling and tempering, and heating and cooling are carried out in a protective environment of chlorides (2).

 The aim of the invention is to increase the operational stability.

The proposed method is carried out performing thermocycling in two stages: first by repeated heating to a temperature of 610 ^C - A _1, followed by rapid cooling in oil, followed by repeated heating and cooling in the temperature range between the melting temperature and the onset temperature of the martensitic transformation, the final quenching temperature last heating during thermal cycling and tempering. In this case, the isothermal extracts at the second stage of thermal cycling are carried out in a melt of chloride salts, to which carbonate and carbide are additionally introduced in the following ratio of components,%: Carbide 4-10 Carbonate 2-10 Melt of chloride salts 80-94
Barium carbonate or potassium carbonate is used as carbonate, and silicon carbide or calcium carbide is used as carbide.

When carrying out the proposed method of heat treatment of tools made of high speed steel, multiple heating with subsequent cooling is carried out both in salt baths and in heating furnaces. Moreover, the maximum heating temperature in a heating furnace is limited by the operating temperature of the furnace, which, as a rule, does not exceed 1000-1100 ^о С. The compositions of salt and alkaline baths designed to operate in a wide temperature range (160-1300 ^о С) are determined by generally accepted standards .

 The maximum and minimum values of the heating and cooling speeds during thermal cycling are limited only by the capabilities of heating devices (salt bath and furnace).

 During thermal cycling at the first stage (at the heating stage), the optimal number of cycles (repetitions of heating and cooling) does not exceed two or three, since a subsequent increase in the cycles impairs the properties of the steel. During thermal cycling at the second stage (at the hardening stage), the optimal number of cycles does not exceed two or three and greatly simplifies the process, since a subsequent increase in the number of cycles does not lead to a large improvement in properties.

Application of the proposed method requires, as well as in traditional tempering, compulsory carrying two or three times tempering (540-560 ^{° C;} 1 hour) to obtain a high strength and a secondary hardness removal quenching stresses and residual austenite transformation to martensite.

Similarly, as with traditional quenching, cooling in oil or in hot environments (200-600 ^о С) provides after tempering the same properties (viscosity, strength, wear resistance).

 The difference in the wear resistance of a tool made of high-speed steel, processed according to the proposed technology, is apparently due to the completeness of all of the above processes that improve the cutting properties of a woodworking tool.

 The proposed method applies to all steels belonging to the class of high-speed, with the only difference being that for each brand of high-speed steel there is its own optimum temperature for heating and cooling during thermal cycling.

 PRI me R. Heat treatment of high-speed steel P18, according to the known and proposed method, was carried out both in bath-furnaces and chamber furnaces.

 The operational durability of the instrument was evaluated by the results of production tests of milling cutters of size 80x60x80 mm made of P18 steel when milling small spikes for joining the wooden parts of the piano case. Milling conditions: cutting speed 43 m / s, feed 20 m / min, cutting depth 5 mm. The durability of the woodworking tool was judged by the number of linear meters of wood before the first regrind of the cutter, and the increase in resistance was evaluated by the ratio of the lengths of linear meters of wood to the blunting of the cutter processed by the known and proposed methods.

 For repeatability of the results of the same heat treatment mode, at least three cutters were tested.

 Heat treatment of mills made of steel P18 according to the proposed method was carried out as follows.

Steel mills R18 dried in an electric furnace at 300 ^{° C} and then subjected to thermal cycling first step of heating by repeated heating in a salt bath having a temperature between 610 and 810 ^o C, t. E. Below the A _1, followed by cooling in oil . Then cutter subjected to thermocycling hardening step by successive spaces in high-salt bath having a temperature of 1240-1310 ^o C, t. E. Below the _Tm. , and in a low-temperature bath having a temperature of 130-1160 ^about With, that is, above M _n . For R18 the steel melting temperature T _m = 1310 ^{° C,} the martensite start temperature M _s = 130 ^{° C,} the polymorphic transformation temperature A ₁ = 810 ^C. Last heating during thermal cycling combined with heating for quenching, and then cooled in the tool quenching medium and subjected to triple tempering.

Thermal cycling in the first stage when heated below A _{1 was} carried out in one salt bath. Thermal cycling in the second stage in the temperature range between M _n and T _{pl was} carried out in two salt baths, and the low-temperature bath with a temperature below A ₁ can be used at both stages of thermal cycling, which simplifies the process.

To carry out repeated heating and cooling in the second stage of thermal cycling using special protective medium and adding carbide carbonate to the melt of chloride salts, in particular at temperatures above 950 ^{° C} - in a bath on the basis of BaCl _2, in the temperature range of 800-950 ^C. - into a bath based on NaCl, at temperatures 515 - 800 ^о С - into a bath based on 30% BaCl ₂ + NaCl + 50% CaCl ₂ . For multiple cooling in the temperature interval 260-540 ^C. using an alkaline bath consisting of 50% KOH, 50% NaOH, the temperature interval 160-280 ^C. using an alkaline bath consisting of 80% KOH and 20% NaOH, below ^about 160 C used heated oil cylinder grade 52.

 The use of saltpeter baths for cooling is undesirable, since transferring a tool with nitrate residues to a high-temperature bathtub may cause an explosion.

 The holding time during repeated heating and cooling of the tool was precisely observed in accordance with generally accepted standards.

 The results of the study of the wear resistance of the cutters are given in table. 1 and 2.

 From the above data it follows that the use of the proposed method of heat treatment of woodworking tools made of high speed steel allows, in comparison with the known, to increase its operational resistance by 1.1-2.1 times.

Steel grade cutters - P18. Heat treatment: thermal cycling + hardening + tempering (560 ^о С, 1 h, 2 times). Cutting conditions: speed 43 m / s, feed 20 m / min, depth 5 mm, the processed material is wood Grade of the steel of the cutter is P18.

Heat treatment: I thermal cycling (710 ^о С 20 ^о С, 2 cycles, oil cooling) + II thermal cycling combined with quenching (1260 ^о С 1110 ^о С, 2 cycles, oil quenching) + tempering (560 ^о С, 1 h , 2 times).

Cutting conditions: speed 43 m / s, feed 20 m / min, depth 5 mm, the processed material is wood. Composition of a special protective environment: on. 87% of the melt from chloride salts + 6% BaCO ₃ + 7% CaC ₂ . (56) Copyright certificate of the USSR N 1014938, cl. C 21 D 9/22, 1983.

USSR copyright certificate
N cl. C 21 D 9/22, 1989, non-public.

Claims (1)

1. METHOD FOR THERMAL TREATMENT OF CUTTING TOOLS FROM QUICK CUT STEEL, including thermocyclic treatment in the interval between the melting temperature and the temperature of martensitic transformation with isothermal holdings in a protective medium containing molten chloride salts, quenching from the temperature of the last heating, which is heated, in order to increase operational stability, thermal cycling is performed prior to the heating in the temperature range 610 - a ₁ and cooled in oil, and isothermal RP G Exposure is carried out in a protective environment, further comprising a carbonate, and carbide in the following ratio, wt. %:
Carbide 4-10
Carbonate 2 - 10
Melt of chloride salts 80 - 94
2. The method according to p. 1, characterized in that silicon carbide or calcium carbide is used as carbide, and barium carbonate or potassium carbonate is used as carbonate.

Images